Microwave dielectric heating of drops in microfluidic devices
"Microwave dielectric heating of drops in microfluidic devices"
David Issadore, Katherine J. Humphry, Keith A. Brown, Lori Sandberg, David A. Weitz, and Robert M. Westervelt
Lab on a Chip Online advance article (2009)
Soft Matter Keywords
microfluidic, emulsion, dielectric heating
The authors present experimental work and simple theory for a microfluidic device that heats water droplets using microwaves. The device relies on dielectic heating to heat the droplets. A time-varying electric field causes the induced and intrinsic dipole moments within the water drop to align. The energy driving this alignment is viscously dissipated as heat in the droplet, leading to an increase in temperature above ambient. Since water has a strong dielectric loss at GHz frequencies, the microwave signal is absorbed much more strongly by the water drop than by the oil, PDMS, and glass.
The schematic in Figure 1 shows that on the same PDMS-glass microfluidic chip, continuous phases of water and fluorocarbon oil are combined to form drops which are then split in half twice to form a population of smaller drops. These smaller drops pass through the microwave heater region, where a 3.0 GHz signal heats the droplets.
Practical Application of Research
The research begins to open up the possibility of localized temperature control in microfluidic systems. Most systems to date have spatial control down to a few centimeters, but this work pushes temperature control to the 100s of microns scale. The heating and cooling of the water droplets occurs on timescales much shorter than previously accessible. With temperature changes of nearly 30 degrees above ambient achievable, the microwave heating paradigm can be applied to biologically relevant systems, including PCR reactions for DNA analysis, as well as protein denaturing studies and enzyme optimization. Combining this rapid heating with the high-throughput capabilities of microfluidic emulsions has the potential to allow researchers to analyze large sample populations of temperature sensitive reactions.
Dielectric Heating of Water Drops On-Chip
written by Donald Aubrecht